You Might Not Have A Palmaris Longus Muscle

Hold your palm up right now. Touch your thumb to your smallest finger, bend your wrist forward, and count the cords that stand up. Most people see two. Some see one.

The thin one in the middle is the tendon of the palmaris longus, a muscle running the whole length of your forearm — and a substantial minority of people are simply built without it.

How many is where this gets interesting. Worldwide the pooled figure is about one in five: 20.25 % across 26 studies (Yammine, Clinical Anatomy, 2013), which the meta-analysis itself notes is higher than the 14-15 % that gets copied around. But that pooled number hides one of the widest population ranges in human anatomy — roughly 2.71 % in East and Southeast African populations, 4.5 % East Asian, 11.3 % African, 26.16 % South and Southeast Asian, 26.3 % Caucasian, 34.13 % Turkish, 41.7 % Arab Middle Eastern. A fifteenfold spread. So "one in five" is a real global average and a bad prediction about you personally, and if your own count disagrees with the video, that is the data, not an error.

The payoff: missing it costs you nothing anyone has been able to measure. When researchers tested 418 people aged 7 to 85, they found no statistically significant difference in grip or pinch strength between those who had the tendon and those who did not (Sebastin et al., J Hand Surg Br, 2005). That is one study on one cohort, so take it as measured rather than settled — but it is exactly why hand surgeons reach for this tendon first when they need a graft. Long, flat, easy to harvest, and losing it does not show up in your hand. The cord that pulls almost nothing is the one that gets woven into somebody's rebuilt ligament.

Two things this video does not claim. It does not say the muscle does nothing — it contributes minimally to wrist flexion, and minimally is not nothing. And it does not say evolution is deleting it: there is no evidence of a directional trend in living populations. It is an old, stable variation, not a disappearance in progress.

Sources:
https://pubmed.ncbi.nlm.nih.gov/23825029/
https://onlinelibrary.wiley.com/doi/10.1002/ca.22289
https://journals.sagepub.com/doi/abs/10.1016/j.jhsb.2005.03.011
https://www.sciencedirect.com/science/article/abs/pii/S0266768105000859
https://pmc.ncbi.nlm.nih.gov/articles/PMC5207290/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10145763/
https://www.physio-pedia.com/Palmaris_Longus